Earlier this month the BBC director general, Mark Thompson, was prompted to post a blog on the BBC website complaining about the "disturbing new tactics".

The BBC said that independent research shows that the overall weekly audience for the BBC's international news services in Iran – including TV and radio services – has risen by 85% between from 3.9 million in 2009 to 7.2 million in 2011.

"These figures are a tremendous tribute to the courage and dedication of BBC Persian journalists in the face of appalling bullying and intimidation by the Iranian authorities," said the BBC director of global news, Peter Horrocks.

The BBC reckons that more than one in 10 Iranians watch BBC Persian TV each week, or 28% of satellite households.

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